This invention relates to an assembly for plugging a heat exchange tube and, more particularly, to such an assembly utilizing an explosively activated casing.
Many current designs of heat exchangers feature the use of a large plurality of heat exchange tubes supported by a tube sheet and adapted to receive primary fluid which is passed in a heat exchange relationship with a secondary fluid flowing over the tubes. During the lifetime of such a heat exchanger, a number of heat exchange tubes often fail due to erosion, corrosion, intergranular attack, and other causes. This could allow the normally separated fluids to come into direct contact with each other and thus diminish the efficiency of the heat exchanger.
The most simple manner of dealing with these types of failures is to disable the particular heat exchange tube by closing it off at both ends in the vicinity of the tube sheet or sheets. This has been done in the past, for example, by welding plugs in the respective ends of the tubes. However, this requires relatively good access to the tubes and results in a weld bead that could become corroded and fail. Mechanically driven plugs have been used, but these are also not without problems since they are difficult to install with any consistency and have a relatively low pullout strength.
Another method of plugging that has been used is to explosively form a tubular plug to the inner wall of the tube by setting off an explosive within the plug to seal it in the tube. This technique is relatively simple and inexpensive, is very effective and does not disturb the integrity of adjacent tubes. However, when the explosive is set off, some debris and polyethylene vapor can easily be deposited on the exposed surfaces. In most applications the debris can easily be cleaned with a wire brush or felt pellets. However, in a nuclear heat exchanger cleaning the debris and polyethylene vapor results in possible exposure to radiation.